The compound of the formula [I] is a known compound, which shows antihypertensive effect, antirheumatic effect, suppresive effect of liver damage, liquefactive effect of sputum, etc. (Japanese Kokai Koho SHO 54-148783 corresponding to U.S. Pat. No. 4,356,183, Japanese Kokai Koho SHO 55-7255 corresponding to U.S. Pat. No. 4,356,183, U.S. Pat. No. 4,046,889, Japanese Kokai Koho SHO-55-51020 corresponding to U.S. Pat. No. 4,241,086, Japanese Pat. No. 1,066,721 corresponding to U.S. Pat. No. 4,305,958 and Japanese Pat. No. 432,636 corresponding to U.S. Pat. No. 3,246,025) U.S. Pat. Nos. 4,053,651, and 4,347,371.
But, disadvantages of the compound of the formula [I] exist in its less stability and/or low solubility in water, and these problems have not been solved.